Polypropylene is a general-purpose plastic with excellent chemical resistance and high moldability, but is inapplicable to products requiring excellent mechanical properties or heat resistance due to drawbacks of poor heat resistance and mechanical strength. In order to overcome these drawbacks, technologies of reinforcing polypropylene with various kinds of organic or inorganic substances have been used. In general, mechanical properties of polypropylene resin can be improved by mixing an inorganic substance such as whisker, talc and glass fiber with a polypropylene resin using a mixing device such as an extruder, so that the polypropylene resin can be used for interior or exterior elements for vehicles.
For example, in a related art, glass fiber, whisker, and talc are the most generally used for a main inorganic filler of interior elements for vehicles, and are added to produce polypropylene composite resins. In this regard, as the amount of inorganic filler added increases, physical properties such as heat resistance and flexural modulus are improved, but impact strength and scratch resistance are deteriorated. Accordingly, in conventional attempts to solve these problems, methods of improving impact strength and imparting slip property to a surface to improve scratch resistance through addition of rubber have been used.
However, just adding rubber and imparting slip property to the surface may cause limited mechanical properties and treatment of an excess of a slip agent to satisfy scratch resistance, and lead to structural drawbacks of appearance defects caused by volatilization during high-temperature molding as well as whitening after molding.
When it comes to technologies relating to inorganic fillers, glass fibers have surface unevenness-associated problems including formation of roughness and fiber lifting on the surfaces of molded elements, and limitations of improvement in impact strength. In addition, whisker and talc can exhibit desired mechanical properties, but have a drawback of lack in scratch resistance which is the main requirement of molded elements.
Accordingly, there is an increasing need for polypropylene composite resin compositions that are capable of manufacturing interior materials for vehicles with excellent scratch resistance as well as superior mechanical properties such as impact strength.
The above information disclosed in this Background section is provided only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.